1. Field of the Invention
The present invention relates to a drive apparatus for an ink jet printer, and more particularly, to a drive apparatus for an ink jet printer using a single motor in which a pickup roller and a convey roller are not powered while a feed roller line-feeds a sheet of paper.
2. Description of the Related Art
Generally, an ink jet printer having a paper feeding direction that is similar to a paper discharge direction, namely a front-insert-front-out (FIFO) type ink jet printer, has a convey roller disposed between a pickup roller and a feed roller to convey picked up paper to the feed roller.
An example of such ink jet printer is shown in FIG. 1. Referring to FIG. 1, the ink jet printer comprises a paper feed cassette 10, a pickup roller 20, a convey roller 30, a feed roller 40, and a printer head 50. The convey roller 30 is rotatably disposed opposite to a pinch roller 31 and the pinch roller 31 is resiliently supported by a pinch spring 32 thereby applying pressure to the convey roller 30 with a predetermined force.
A plurality of sheets 11 stacked in the paper feed cassette 10 is separated sheet-by-sheet by the pickup roller 20 and a separating wall 12, and the separated sheet 11 enters between the convey roller 30 and the pinch roller 31 along the separating wall 12. The sheet 11′ entered between the convey roller 30 and the pinch roller 31 is conveyed to the feed roller 40 by the rotation of the convey roller 30. Having entered to the feed roller 40, the sheet 11′ is conveyed to below the printer head 50 by the rotation of a friction roller 41 disposed above the feed roller 40. A paper guide 52 is disposed below the printer head 50, and the sheet 11′ enters between the printer head 50 and the paper guide 52. When the sheet 11′ is positioned on the paper guide 52, the printer head 50 sprays ink traveling along a guide bar 51 by a moving belt 53 thereby printing an image on the sheet 11′. When the printing is completed, the sheet 11′ with an image printed thereon is disposed outside by a discharge roller 60.
The feed roller 40 feeds the sheet 11′ onto the paper guider 52 in increments that are as wide as the width of a swath of ink droplets the printer head 50 is able to print, stops until the corresponding swath is completely printed by the printer head 50, and repeats feeding the sheet 11′ in increments (hereinafter called line-feeding). Accordingly, the feed roller 40 is driven by a separate motor and the rotating angle of the feed roller 40 is precisely controlled by a rotation detecting sensor such as a rotary encoder.
Recently, however, a development has been made to provide an ink jet printer which removed a motor to drive the convey roller 30 and added a power transferring apparatus (not shown) to transfer power of the feed roller 40 to the convey roller 30 thereby driving the feed roller 40 and the convey roller 30 using a single motor.
Although the driving mechanism of an ink jet printer using a single motor to drive the convey roller 30 and the feed roller 40 theoretically has the same driving speed for the feed roller 40 and the convey roller 30, in practice the speeds of the paper passing the feed roller 40 and the convey roller 30 are often different. That is, when a sheet of paper is simultaneously passing the feed roller 40 and the convey roller 30, the sheet may be exposed to tension and compression depending on the speed of each the feed roller 40 and the convey roller 30. That is because the coefficient of friction of the surfaces of the feed roller 40 and the convey roller 30 can not be absolutely equal and mechanical errors such as backlash in the power transferring apparatus transferring power from the motor to the convey roller 30 and the feed roller 40 are different.
If the sheet of paper fed by the feed roller is affected by the convey roller, line-feeding of the sheet of paper by the feed roller cannot be controlled precisely as convey failure occurs while the feed roller conveys the sheet of paper. The convey failure occurs as a sheet of paper slips between the feed rollers due to the difference in speed between the feed roller and the convey roller. If the sheet of paper is not line-fed precisely by the feed roller, printing quality may be impaired. Therefore, in order to improve printing quality of an ink jet printer with the feed roller and the convey roller driven by a single motor, it is necessary to not to transfer power to the convey roller thereby preventing the convey roller from rotating while the feed roller line-feeds a sheet of paper.